A hydraulic disk brake is known, which is configured to supply hydraulic pressure generated in a hydraulic master cylinder or hydraulic pressure accumulated in an accumulator to a wheel cylinder provided to each wheel, according to a brake pedal operation value, thereby generating a regular braking force. With such a hydraulic disk brake, a friction pad is pressed into contact with a disk rotor by driving a piston via hydraulic pressure. Also, a conventional technique has been proposed in which such a wheel cylinder piston is also shared with a parking brake apparatus. For example, a disk brake has been proposed including a parking brake mechanism which operates using an electric motor as a driving source provided outside the wheel cylinder so as to hold the piston at a braking position (see Patent document 1, for example). That is to say, such a disk brake is configured to use both the hydraulic operating mechanism and the mechanical operating mechanism to drive the piston.